linux-kernel - Re: [PATCH v7 RESEND 2/4] kexec: allocate unencrypted control pages for kdump in case SME is enabled

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Message-ID: <20180927165323.GC19779@zn.tnic>
Date:   Thu, 27 Sep 2018 18:53:23 +0200
From:   Borislav Petkov <bp@...e.de>
To:     Lianbo Jiang <lijiang@...hat.com>
Cc:     linux-kernel@...r.kernel.org, kexec@...ts.infradead.org,
        tglx@...utronix.de, mingo@...hat.com, hpa@...or.com,
        x86@...nel.org, akpm@...ux-foundation.org,
        dan.j.williams@...el.com, thomas.lendacky@....com,
        bhelgaas@...gle.com, baiyaowei@...s.chinamobile.com, tiwai@...e.de,
        brijesh.singh@....com, dyoung@...hat.com, bhe@...hat.com,
        jroedel@...e.de
Subject: Re: [PATCH v7 RESEND 2/4] kexec: allocate unencrypted control pages
 for kdump in case SME is enabled

On Thu, Sep 27, 2018 at 03:19:52PM +0800, Lianbo Jiang wrote:
> When SME is enabled in the first kernel, we will allocate unencrypted pages
> for kdump in order to be able to boot the kdump kernel like kexec.

This is not what the commit does - it marks the control pages as
decrypted when SME. Why doesn't the commit message state that and why is
this being done?

> Signed-off-by: Lianbo Jiang <lijiang@...hat.com>
> Reviewed-by: Tom Lendacky <thomas.lendacky@....com>
> ---
>  kernel/kexec_core.c | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
> 
> diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c
> index 23a83a4da38a..e7efcd1a977b 100644
> --- a/kernel/kexec_core.c
> +++ b/kernel/kexec_core.c
> @@ -471,6 +471,16 @@ static struct page *kimage_alloc_crash_control_pages(struct kimage *image,
>  		}
>  	}
>  
> +	if (pages) {
> +		/*
> +		 * For kdump, we need to ensure that these pages are
> +		 * unencrypted pages if SME is enabled.

Remember to always call unencrypted pages "decrypted" - this is the
convention we agreed upon and it should keep the confusion level at
minimum to others staring at this code.

> +		 * By the way, it is unnecessary to call the arch_
> +		 * kexec_pre_free_pages(), which will make the code
> +		 * become more simple.
> +		 */

This second sentence I don't understand...

> +		arch_kexec_post_alloc_pages(page_address(pages), 1 << order, 0);
> +	}
>  	return pages;
>  }
>  
> @@ -867,6 +877,7 @@ static int kimage_load_crash_segment(struct kimage *image,
>  			result  = -ENOMEM;
>  			goto out;
>  		}
> +		arch_kexec_post_alloc_pages(page_address(page), 1, 0);
>  		ptr = kmap(page);
>  		ptr += maddr & ~PAGE_MASK;
>  		mchunk = min_t(size_t, mbytes,
> @@ -884,6 +895,7 @@ static int kimage_load_crash_segment(struct kimage *image,
>  			result = copy_from_user(ptr, buf, uchunk);
>  		kexec_flush_icache_page(page);
>  		kunmap(page);
> +		arch_kexec_pre_free_pages(page_address(page), 1);
>  		if (result) {
>  			result = -EFAULT;
>  			goto out;
> -- 
> 2.17.1
> 

-- 
Regards/Gruss,
    Boris.

SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg)